Not a complete solution, but I'll try to help get the ball rolling.
I didn't come up with a slider, but let's assume for now there's already a working one. You said the position is between 0-100, but for this I'll use 0-1 and call it x. (If you want to stick with a percent, it just requires dividing or multiplying somewhere along the line.) So, you position A at x=0 and B at x=1. And at 0<x<1, when the slider is in between, you will be at C.
Start of by getting the vector between A and B, I'll call it AB. So you'll need to create a vector3 for each, as well as C.
To get AB use "set vector value" of AB to be the same as B, then use "subtract Vector3" to subtract A from AB, to give your actual AB value. (ie B-A=AB)
So, now if you multiply AB by some number between zero and one and add it to A, you will get a position between A and B.
So, use "Vector 3 multiply" and multiply by your int, x.
Then use "Vector 3 add" to add to A. i.e. A+xAB=C
Then "set position" of your object to C.
Seemed to work in my testing. But it sure reminded me how rusty my geometry is. Hope it helps at all.